Enzyme graph
Enzymes are proteins that function properly in a very specific temperature range.
When a certain temperature is exceeded (this temperature depends on the particular enzyme), the bonds between its monomers, the amino acids, become unstable and can cause its denaturation, i.e it loses its primary structure, and with it its enzymatic function.
With this information, it can be deduced that the correct answer to this question is the first option: The structure of the enzymes changes.
